This invention relates to molding compositions.
Reaction injection molding ("RIM") is a molding process in which one or more liquid or blending reactants are metered separately to a mixing head which combines them e.g., by high-impingement mixing. The mixture then is injected into a mold where it polymerizes to form a molded part. In structural reaction injection molding ("SRIM"), which is often referred to as reinforced reaction injection molding ("RRIM"), reinforcements such as chopped glass fiber or particulate mineral fillers are added to the mixture prior to molding. In another type of SRIM process, a low viscosity, partially polymerized RIM composition is injected into a mold filled with woven fiber mat, and the resulting composition molded. In both the RIM and SRIM processes, the molded parts are coated prior to use to provide ultraviolet protection and to match other parts.
A second type of molding process involves premix. Premix is a molding composition prepared prior to and apart from the molding operation which contains all the components necessary for molding, e.g., resin, reinforcing agents, fillers, catalysts, release agents, etc. One type of premix is called sheet molding compound ("SMC"). SMC is a thin, semi-tacky sheet of thermosetting resin typically reinforced with chopped or continuous strand glass fibers. The sheet can be molded to form a variety of parts using, e.g., matched die molding techniques. A second type of premix is called bulk molding compound ("BMC"). BMC is prepared in the form of a putty that can be directly molded. It can also be extruded in the form of a bar or log to facilitate handling. Like the RIM and SRIM molded products, the molded premix products also are often coated prior to use.
Carbon fibrils are carbon filaments having diameters less than 500 nanometers. Examples of particular carbon fibrils and methods for preparing them are described in the above-referenced Snyder et al. application; Tennent, U.S. Pat. No. 4,663,230 ("Carbon Fibrils, Method for Producing Same and Compositions Containing Same"); Tennent et al., U.S. Ser. No. 871,676 filed Jun. 6, 1989 ("Novel Carbon Fibrils, Method for Producing Same and Compositions Containing Same"); Tennent et al., U.S. Ser. No. 871,675 filed Jun. 6, 1986 ("Novel Carbon Fibrils, Method for Producing Same and Encapsulated Catalyst"); Mandeville et al., U.S. Ser. No. 285,817 filed Dec. 16, 1988 ("Fibrils"); and McCarthy et al., U.S. Ser. No. 351,967 filed May 15, 1989 ("Surface Treatment of Carbon Microfibers"), all of which are assigned to the same assignee as the present application and are hereby incorporated by reference in their entirety.